- Photic generation of 11-cis-retinal in bovine retinal pigment epithelium
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Photoisomerization of the 11-cis-retinal chromophore of rod and cone visual pigments to an all-trans-configuration is the initiating event for vision in vertebrates. The regeneration of 11-cis-retinal, necessary for sustained visual function, is an endergonic process normally conducted by specialized enzyme systems. However, 11-cis-retinal also can be formed through reverse photoisomerization from all-trans-retinal. A nonvisual opsin known as retinal pigment epithelium (RPE)-retinal G-protein- coupled receptor (RGR) was previously shown to mediate visual chromophore regeneration in photic conditions, but conflicting results have cast doubt on its role as a photoisomerase. Here, we describe high-level production of 11-cis-ret-inal from RPE membranes stimulated by illumination at a narrow band of wavelengths. This activity was associated with RGR and enhanced by cellular retinaldehyde-binding protein (CRALBP), which binds the 11-cis-retinal produced by RGR and prevents its re-isomerization to all-trans-retinal. The activity was recapitulated with cells heterologously expressing RGR and with purified recombinant RGR. Using an RGR variant, K255A, we confirmed that a Schiff base linkage at Lys-255 is critical for substrate binding and isomerization. Single-cell RNA-Seq analysis of the retina and RPE tissue confirmed that RGR is expressed in human and bovine RPE and Müller glia, whereas mouse RGR is expressed in RPE but not in Müller glia. These results provide key insights into the mechanisms of physiological retinoid photoisomerization and suggest a novel mechanism by which RGR, in concert with CRALBP, regenerates the visual chromophore in the RPE under sustained light conditions.
- Zhang, Jianye,Choi, Elliot H.,Tworak, Aleksander,Salom, David,Leinonen, Henri,Sander, Christopher L.,Hoang, Thanh V.,Handa, James T.,Seth Blackshaw,Palczewska, Grazyna,Kiser, Philip D.,Krzysztof Palczewski
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Read Online
- Stereoselective synthesis of 11Z-retinal by use of tricarbonyliron complex
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Peterson reaction of 7E,9E-β-ionylideneacetaldehyde-tricarbonyliron complex with ethyl trimethylsilyl acetate afforded Z-olefin in high stereoselectivity, which was converted to the corresponding 11Z-retinal in excellent yield.
- Wada, Akimori,Tanaka, Yukiko,Fujioka, Naoko,Ito, Masayoshi
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Read Online
- Stimulatory effect of cyanidin 3-glycosides on the regeneration of rhodopsin
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Anthocyanins have been suggested to improve visual functions. This study examined the effect of four anthocyanins in black currant fruits on the regeneration of rhodopsin using frog rod outer segment (ROS) membranes. Cyanidin 3-glycosides, glucoside and rutinoside, stimulated the regeneration, but the corresponding delphinidins showed no significant effect. The formation of a regeneration intermediate was suggested to be accelerated by cyanidin 3-rutinoside. Their effects on the cGMP-phosphodiesterase activity in the ROS membranes were also investigated but found to be negligible. It was concluded that the major effect of anthocyanins in rod photoreceptors is on the regeneration of rhodopsin.
- Matsumoto, Hitoshi,Nakamura, Yuko,Tachibanaki, Shuji,Kawamura, Satoru,Hirayama, Masao
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Read Online
- Z -isomerization of retinoids through combination of monochromatic photoisomerization and metal catalysis
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Catalytic Z-isomerization of retinoids to their thermodynamically less stable Z-isomer remains a challenge. In this report, we present a photochemical approach for the catalytic Z-isomerization of retinoids using monochromatic wavelength UV irradiation treatment. We have developed a straightforward approach for the synthesis of Z-retinoids in high yield, overcoming common obstacles normally associated with their synthesis. Calculations based on density functional theory (DFT) have allowed us to correlate the experimentally observed Z-isomer distribution of retinoids with the energies of chemically important intermediates, which include ground- and excited-state potential energy surfaces. We also demonstrate the application of the current method by synthesizing gram-scale quantities of 9-cis-retinyl acetate 9Z-a. Operational simplicity and gram-scale ability make this chemistry a very practical solution to the problem of Z-isomer retinoid synthesis.
- Kahremany, Shirin,Sander, Christopher Lane,Tochtrop, Gregory P.,Kubas, Adam,Palczewski, Krzysztof
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supporting information
p. 8125 - 8139
(2019/09/19)
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- Substrate specificity and subcellular localization of the aldehyde-Alcohol redox-Coupling reaction in carp cones
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Our previous study suggested the presence of a novel conespecific redox reaction that generates 11-cis-retinal from 11-cisretinol in the carp retina. This reaction is unique in that 1) both 11-cis-retinol and all-trans-retinal were required to produce 11-cis-retinal; 2) together with 11-cis-retinal, all-trans-retinol was produced at a 1:1 ratio; and 3) the addition of enzyme cofactors such as NADP(H) was not necessary. This reaction is probably part of the reactions in a cone-specific retinoid cycle required for cone visual pigment regeneration with the use of 11-cis-retinol supplied from Mueller cells. In this study, using purified carp cone membrane preparations, we first confirmed that the reaction is a redox-coupling reaction between retinals and retinols. We further examined the substrate specificity, reaction mechanism, and subcellular localization of this reaction. Oxidation was specific for 11-cis-retinol and 9-cis-retinol. In contrast, reduction showed low specificity: many aldehydes, including all-trans-, 9-cis-, 11-cis-, and 13-cis-retinals and even benzaldehyde, supported the reaction. On the basis of kinetic studies of this reaction (aldehyde-alcohol redox-coupling reaction), we found that formation of a ternary complex of a retinol, an aldehyde, and a postulated enzyme seemed to be necessary, which suggested the presence of both the retinol- and aldehydebinding sites in this enzyme. A subcellular fractionation study showed that the activity is present almost exclusively in the cone inner segment. These results suggest the presence of an effective production mechanism of 11-cis-retinal in the cone inner segment to regenerate visual pigment.
- Sato, Shinya,Fukagawa, Takashi,Tachibanaki, Shuji,Yamano, Yumiko,Wada, Akimori,Kawamura, Satoru
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p. 36589 - 36597
(2014/01/17)
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- Cross-coupling reactions of organosilicon compounds in the stereocontrolled synthesis of retinoids
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This paper presents a full account of the use of Hiyama cross-coupling reactions in a highly convergent approach to retinoids in which the key step is construction of the central C10-C11 bond. Representatives of two families of oxygen-activated dienyl silanes (ethoxysilanes and silanols) and of all reported families of "safety-catch" silanols (siletanes, silyl hydrides, allyl-, benzyl-, aryl-, 2-pyridyl- and 2-thienylsilanes) were regio- and stereoselectively prepared and stereospecifically coupled to an appropriate electrophile by treatment with a palladium catalyst and a nucleophilic activator. Both all-trans and 11-cis-retinoids, and their chain-demethylated analogues, were obtained in good yields regardless of the geometry (E/Z) and of the steric congestion in each fragment. This comprehensive study conclusively establishes the Hiyama cross-coupling reaction, with its mild reaction conditions and stable, easily prepared, ecologically advantageous silicon-based coupling partners, as the most effective route to retinoids reported to date.
- Bergueiro, Julian,Montenegro, Javier,Cambeiro, Fermin,Saa, Carlos,Lopez, Susana
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supporting information; experimental part
p. 4401 - 4410
(2012/06/01)
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- Synthesis of 11-cis-retinoids by hydrosilylation-protodesilylation of an 11,12-didehydro precursor: Easy access to 11- and 12-mono- and 11,12-dideuteroretinoids
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An expeditious, highly efficient approach to 11-cis-retinoids was achieved by semihydrogenation of a readily available 11-yne precursor through a hydrosilylation-protodesilylation protocol. The complete chemo-, regio-, and syn-stereoselectivity of the method also allowed direct access to 11- and 12-monodeutero-, and 11,12-dideutero-11-cis-retinoids. The analogous trans series was not accessible by this route, and was synthesized by means of Hiyama coupling. Copyright
- Bergueiro, Julián,Montenegro, Javier,Saá, Carlos,López, Susana
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supporting information
p. 14100 - 14107
(2013/01/15)
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- Syntheses of 13C2-labelled 11Z-retinals
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To enable solid-state NMR investigations of the rhodopsin chromophore and its photointermediates, a series of 11Z-retinal isotopomers have been synthesised containing pairs of adjacent 13C labels at C9/C10, C10/C11 or C11/C12, respectively. The C9 labelled carbon atom was introduced through the Heck reaction of a 13C-labelled Weinreb acrylamide derivative, and the label at the C12 position derived from a 13C-containing ethoxy Bestmann-Ohira reagent. The 13C labels at C10 and C11 were introduced through the reaction of β-ionone with labelled triethyl phosphonoacetate.
- McLean, Neville J.,Gansmuller, Axel,Concistre, Maria,Brown, Lynda J.,Levitt, Malcom H.,Brown, Richard C.D.
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supporting information; experimental part
p. 8404 - 8410
(2011/11/12)
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- Hiyama cross-coupling reaction in the stereospecific synthesis of retinoids
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The first application of the Hiyama reaction to the synthesis of retinoids is reported. A range of organosilicon moieties (siloxanes, silanols and three kinds of "safety-catch" silanols) were successfully coupled, under activation, to obtain trans-retinol or 11-cis-retinol with high yield and stereoselectivity. The advantageous properties of the silicon-based coupling partners and the mild reaction conditions firmly establish the Hiyama reaction as a viable (even superior) alternative to the traditional Suzuki and Stille couplings in the retinoid field.
- Montenegro, Javier,Bergueiro, Julian,Saa, Carlos,Lopez, Susana
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body text
p. 141 - 144
(2009/07/04)
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- Highly convergent, stereospecific synthesis of 11-cis-retinoids by metal-catalyzed cross-coupling reactions of (Z)-1-alkenylmetals
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(Chemical Equation Presented) A stereospecific synthesis of 11-cis-retinoids has as its key step the hitherto unexplored palladium-catalyzed cross-coupling of trans-tnenyl electrophiles and (1Z,3E)-penta-1,3-dienyl boronates (a Suzuki-Miyaura reaction) or
- Lopez, Susana,Montenegro, Javier,Saa, Carlos
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p. 9572 - 9581
(2008/04/05)
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- 9-Demethyl-9-haloretinals by Wadsworth-Emmons coupling - Easy preparation of pure (all-E), (9Z) and (11Z) isomers
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5-(2′,6′,6′-Trimethyl-1′-cyclohexen-1′-yl) -4-penten-2-yn-1-al has been prepared in a one-pot process starting from β-ionone in almost quantitative yield. Using 1,4-nucleophilic addition reactions, the corresponding 9-Cl, 9-Br, 9-1 β-ionylideneacetaldehyde systems could be obtained in one step in quantitative yield as a mixture of (9Z) and (all-E) isomers. Even the corresponding fluoro derivative could be obtained in good yield as (9Z) and (all-E) isomers. In the case of a double bond having a halogen substituent, the IUPAC rules have the (E) nomenclature for a cis double bond and the (Z) for a trans double bond. Simple column chromatography gave the pure (9Z) and (all-E) form. Optimizing the Wadsworth-Emmons coupling gave the corresponding (all-E)- and (9Z)-retinonitriles in quantitative yield. Subsequent DIBAL-H reduction gave the corresponding retinals. For the preparation of the (UZ) isomers essential to vision, we found that Wadsworth-Emmons reactions with the diphenyl phosphonate group gave retinonitriles in quantitative yield, where the newly formed double bond is predominantly the (11Z) form (> 60%), together with the (9Z) isomer as minor component. The nitriles could be isolated in pure (9Z.11Z) and (9Z) forms by simple column chromatography. In the case of the (9Z,11Z)-9-demethyl-9-halo systems, a complication arose due to the unprecedented acid lability of these (9Z,11Z) aldehydes. By adjusting the DIBAL-H reduction workup procedure, these aldehydes are now available in pure form. We used this strategy to rationally synthesize (11Z)-retinal starting from β-cyclocitral as a first test for the generality of our new approach. β-Ionylideneacetaldehyde could be prepared in the (all-E) form in almost quantitative yield. Extending the conjugated chain of this molecule gave an almost quantitative yield of a mixture containing 80% (11Z)-retinal and 20% (all-E) as the minor component. Simple column chromatography gave pure (11Z)-retinal in 75% overall yield. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.
- Wang, Yajie,Woo, Wei Sein,Van Der Hoef, Ineke,Lugtenburg, Johan
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p. 2166 - 2175
(2007/10/03)
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- Selective isomerization of retinal upon two-photon excitation
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The products of photo-isomerization when excited directly up to the two-photon-allowed 1Ag- excited state of alltrans and five cis isomers of retinal were determined. The composition of the isomers at the photo-stationary state was drastically changed as compared to one-photon excitation. The production of the 13-cis isomer was selectively increased, and the production of the dicis isomers was observed in the case of a direct excitation upon the 31Ag- state, although they were hard to be produced by one-photon excitation in n-hexane solution. These results clearly evidenced that there exist isomerization pathways via two-photon-allowed excited states.
- Sashima, Tokutake,Hashimoto, Hideki,Koshihara, Shin-ya
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p. 380 - 385
(2007/10/03)
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- A Highly Stereoselective Synthesis of 11Z-Retinal Using Tricarbonyliron Complex
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A stereoselective synthesis of 11Z-retinal 2, which is the chromophore of visual pigment (rhodopsin), was accomplished from the β-ionylideneacetaldehyde-tricarbonyliron complex 3. The Peterson reaction of 3 using ethyl trimethylsilylacetate smoothly proce
- Wada, Akimori,Fujioka, Naoko,Tanaka, Yukiko,Ito, Masayoshi
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p. 2438 - 2443
(2007/10/03)
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- Efficient synthesis of 11-cis-retinoids
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The light sensitivity and unstable nature of 11-cis-retinoids makes them ideal visual chromophores in nature. The synthesis of 11-cis-retinal analogues is of paramount importance in bioorganic studies of rhodopsin, the photoreceptor of the visual transduction pathway, but the instability of 11- cis-retinoids complicates their synthesis and there is no general synthetic route. Common strategies to the cis geometry have failed in the case of 11- cis-retinoids, and most often low yields and complex isomeric mixtures are obtained. Herein we report an efficient, general, and mild preparation of 11- cis-retinoids by semi-hydrogenation of 11-yne-retinoid precursors with Cu/Ag- activated zinc dust.
- Borhan, Babak,Souto, Maria L.,Um, Joann M.,Zhou, Bishan,Nakanishi, Koji
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p. 1172 - 1175
(2007/10/03)
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- Contribution of methyls in retinal side chain to regioselective photoisomerization of retinochromes
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All-trans-9-demethyl-11-methylretinal was synthesized to elucidate the chromophoric interaction between hydrophobic part in retinochrome and 9-methyl substituent of retinal. Photoirradiation of its pigment efficiently gave the 11-cis-isomer in 90% regiose
- Tsujimoto, Kazuo,Sugiura, Jun'ichirou,Takemori, Nobuaki,Mizukami, Taku
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p. 1051 - 1052
(2007/10/03)
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- Vinyltin acetals in terpenic and nor-terpenic synthesis
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Vinyltin acetals obtained by stannylmetallation of homopropargyl acetals with Bu3SnMgMe/CuCN (E configuration) or by titanation of the corresponding alkyltin acetals (Z configuration) have been proved to be efficient storable precursors for the stereoselective synthesis of terpenoids, under mild experimental conditions.Due to the presence of a nucleophilic centre (Csp2-Sn bond) and of a protected electrophilic centre, they are also useful intermediates for an iterative synthesis of retinal and nor-retinoids. - Keywords: vinyltin; acetal; vinyllithium; monoterpenoid; retinal; nor-retinoid
- Launay, Valerie,Beaudet, Isabelle,Quintard, Jean-Paul
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p. 937 - 946
(2007/10/03)
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- Retinal isomer composition in some bacteriorhodopsin mutants under light and dark adaptation conditions
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The isomeric composition of retinal was measured in a number of bacteriorhodopsin (bR) mutants (D85N), D212N, R82A, Y185F, and D115N) under various conditions, using a rapid retinal extraction technique followed by HPLC analysis. Besides the 13-cis and the all-trans retinal isomers observed in wild type (wt) bR under physiological conditions, the 11-cis and 9-cis retinal isomers were observed in variable but minor amounts in the bR mutants. In addition, the values of the equilibrium constant at two temperatures and the enthalpy change for the all-trans to 13-cis isomerization process in the dark-adapted state of D212N, D85N, deionized blue bR, and wt bR were determined. We find that perturbation of the retinal cavity (pocket) by residue replacement changes the relative thermal stability of the different retinal isomers, allowing for thermal-and/or photoisomerization of the retinal chromophore along C9-C10 and C11-C12 bonds to moderately compete with the isomerization around the C13-C14 bond. The bR mutants expressed in Halobacterium salinarium studied in the present work showed normal 13-cis to all-trans light adaptation, in contrast with abnormal all-trans to 13-cis light adaptation observed for D212E, D212A, and D212N expressed in Escherichia coli, suggesting an influence of the purple membrane lattice and/or the lipids on the stability of the different retinal isomers within the protein.
- Song,Yang,El-Sayed,Lanyi
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p. 10052 - 10055
(2007/10/02)
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- Low-Valent Titanium Reductive Elimination: a Direct and Highly Stereoselective Synthesis of Vitamin A Aldehyde.
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It was shown that the low-valent titanium reductive elimination could be carried out in presence of a thioacetal group.An application to the synthesis of vitamin A aldehyde is described.
- Solladie, Guy,Berl, Valerie
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p. 3477 - 3480
(2007/10/02)
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- A new prenylation method using the lithium enolate of prenal. Reaction with polyunsaturated aldehydes. A short access to retinal
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The enolate of prenal 1 prepared from the corresponding silyl enol ether 2 or enol acetate 3 led to a γ-regiospecific reaction with polyunsaturated aldehydes 4 yielding dihydropyrans 5 leading after hydrolysis to polyenals 7. This process allows the introduction of the isoprenyl skeleton. A synthesis of retinal, from β-ionylidenacetaldehyde is reported.
- Duhamel, Lucette,Guillemont, Jerome,Poirier, Jean-Marie,Chabardes, Pierre
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p. 4499 - 4500
(2007/10/02)
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- Photoisomerization of Hindered Poly-cis Isomers of Retinal. Regioselectivity And One -Photon-Multiple-Bond Isomerization.
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Direct irradiation of five dicis (7,9, 7,11, 7,13, 9,11 and 9,13) and one tricis (7,9,11) isomers of retinal led to regioselective isomerization at the 13,14 bond as well as multiple-bond isomerization.
- Ganapathy, Srinivasan,Liu, Robert S. H.
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p. 6957 - 6960
(2007/10/02)
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- β-Lactoglobulin Directed Photoisomerization of Retinal and Related Compounds
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The 11-cis enriched photostationary state mixture of retinal trapped in BLG, a water soluble protein, is similar to that of retinal in heptanol.The results, along with those of the lower homologs, are consistend with a model involving specific protein interaction with the cyclohexenyl portion of the substrate and remote protonation of the aldehyde carbonyl group.
- Li, Xiao-yuan,Asato, Alfred E.,Liu, R. S. H.
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p. 4841 - 4844
(2007/10/02)
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- 8,16- And 8,18-methanobacteriorhodopsin. Synthesis and spectroscopy of 8,16- and 8,18-methanoretinal and their interaction with bacterioopsin
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8,16- And 8,18-methanoretinal with a locked 6-s-trans and a 6-s-cis conformation have been synthesized and characterized.Their 9-Z and 13-Z isomers could also be prepared, in contrast to the 11-Z. 8,16-Methanoretinal easily binds with bacterioopsin (bO) to form a bacteriorhodopsin analogue which closely resembles natural bacteriorhodopsin (bR) (λmax, light-dark adaptation and proton pump action).The interaction of 8,18-methanoretinal with bO is complex.These findings give additional support to the fact that in bR the chromophore occurs in the planar 6-s-trans conformation.Approximately 1200 cm-1 of the opsin shift in bR (5100 cm-1) arises because the chromophore changes upon binding to the protein from a 40 deg twisted 6-s-cis to a planar 6-s-trans conformation.Both 8,16- and 8,18-methano bR have a ca. 3900 cm-1 opsin shift, since the C6-C7 conformation does not allow protein-induced changes.This is consistent with the idea that the opsin shift is mainly due to the perturbation of the Schiff base region.
- Steen, R. van der,Biesheuvel, P. L.,Erkelens, C.,Mathies, R. A.,Lugtenburg, J.
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- Sensitized photoisomerization of all-trans- and 11-cis-retinal
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The photoisomerization of all-trans-retinal (all-trans) and 11-cis-retinal (11-cis) sensitized by a range of sensitizers (porphyrins, Zn-porphyrins, naphthacene and a Zn-phthalocyanine) with varying triplet energies above and below the vertical triplet energy of all-trans-retinal (E(T) = 149 kJ/mol) has been investigated by continuous illumination and HPLC analysis of the products. The composition of the photostationary states, the relative isomerization quantum yields of all-trans and 11-cis, and the primary product ratios are reported. One photon-one bond isomerizations are dominant. With Zn-TPP as sensitizer it is shown that 11-cis and possibly all-trans undergoes one photon-two bond isomerizations as well. The quantum yields of photoisomerization of 11-cis sensitized by biphenyl (E(T) = 275 kJ/mol) and anthracene (E(T) = 178 kJ/mol) were found to be identical. Absolute measurements allowed evaluation of the overall triplet isomerization quantum yield of 11-cis, Φ(iso)(T)(11-cis→) = 1.0 ± 0.2, from which the corresponding quantity for all-trans, Φ(iso)(T)(trans-→) = 0.15 ± 0.05, was obtained. The overall photoisomerization quantum yield of 11-cis with direct excitation at 254 nm was determined as Φ(iso)(d)(11-cis→) = 0.42 ± 0.05 assuming all-trans and 13-cis to be the primary products. Quenching rate constants of several of the sensitizer triplet states by retinal were measured by laser flash photolysis. Possible mechanisms that could account for the experimental results are discussed, and it is concluded that the photoisomerizations most likely involve the retinal triplet states as intermediates. Within this model the observed sensitizer triplet energy dependence of the primary product ratios suggests that the triplet states of the different retinal isomers are different mixtures of triplet excited species, and that the composition of these mixtures depends on the starting isomers as well as on the sensitizer triplet energy for energies below the vertical triplet energy of all-trans-retinal. In the light of a review of the existing literature on the direct and the sensitized photoisomerization of retinals these conclusions suggest substantial corrections to the accepted picture of retinal photochemistry.
- Jensen,Wilbrandt,Bensasson
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p. 7877 - 7888
(2007/10/02)
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- A MODEL STUDY OF REGENERATION PROCESS IN RHODOPSIN VISUAL CYCLE
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The regeneration process in rhodopsin was studied by an estimation of isomer population at photoequilibrium for the model compounds of N-retinylidene phosphatidylethanolamine.We suggested that the preferential formation of 11-cis isomer may be induced by the through-bond effect of oxygen atom of imine moiety of a Schiff base.
- Sakurai, Minoru,Shirota, Osamu,Inoue, Yoshio,Chujo, Riichiro
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p. 167 - 170
(2007/10/02)
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- Studies on the Catalyzed Interconversions of Vitamin A Derivatives
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The kinetics of the I2-catalyzed isomerization of the retinal isomers were studied.The all-trans isomer formed 13-cis-retinal rapidly with a rate constant 1.9E-4 s-1.The reverse reaction occurred with a rate constant of 4.5E-4 s-1.The 11-cis isomer was first converted to all-trans-retinal with a rate constant of 3.1E-4 s-1, although the 13-cis isomer was also rapidly formed.The 9-cis isomer was isomerized to the 9-cis, 13-cis isomer before the other isomers were generated and the 13-cis isomer was converted to its all-trans congener prior to the formation of the other isomers.Similar results appear to occur when other methods of catalysis are used.This isomerization about the C13-C14 double bond appears to be kinetically favored event, eliminating the possibility that 11-cis might be a kinetic product formed from the all-trans isomer.At equilibrium, only 0.1percent of 11-cis-retinal is found.Equilibration of all-trans-retinol palmitate also generated very little of the 11-cis-isomer (/= 0.2percent) 11-cis-retinol palmitate at equilibrium.The implications of these results for an 11-cis-retinal regeneration mechanism in the eye are discussed.
- Rando, Robert R.,Chang, Andrew
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p. 2879 - 2882
(2007/10/02)
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- Silica Gel Mediated Photoisomerization of Retinal Isomers and Comparisons with Other Forms of Environmental Pertubation
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The electronic spectra and photoreactivity of slurries of retinal isomers, prepared by adsorbing the isomers onto wet silica gel and suspending the support in cyclohexane, have been investigated.Adsorption of 9-cis-, 11-cis-, 13-cis-, and all-trans-retinal is accompanied by an ca. 3000-cm-1 red shift of their lowest energy absorption band maxima relative to their band positions in homogeneous cyclohexane solution.Irradiation of the slurries at 514.5 nm, a wavelength inefficiently absorbed in the absence of silica gel, leads to reasonably efficient photoisomerization of each of these isomers.Prolonged photolysis yields a mixture of the four isomers that is photostationary with respect to relative concentrations and richest in 11-cis-retinal, which constitutes ca. 35percent of this mixture.Although small quantities of other isomers are present, the photostationary composition of the heterogeneous photolysate can be predicted with reasonable accuracy from the relative absorptivities and primary photoprocesses of the four principal isomers comprising the photolysate.Comparisons with primary photoprocesses reported for retinal isomers in polar and nonpolar solvents reveal that adsorption onto silica gel can result in novel patterns of photoisomerization.Complementary comparisons are made with the electronic spectra and photoreactivity of adducts formed in hydrocarbon solution from retinal isomers and a lanthanide β-diketonate complex.The excited-state properties of these various retinal-based systems highlight the impotance of environment in controlling photoreactivity.Steric and electronic factors that may contribute to the observed features of silica gel mediated photoisomerization are discussed in this context.
- Zawadzki, Mary E.,Ellis, Arthur B.
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p. 3156 - 3161
(2007/10/02)
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- Thermal Sigmatropic Rearrangements of Vinylallenes Leading to 11-cis-Retinoids and the Novel Properties of 9-cis,11-cis,13-cis-Retinal and 11-cis,13-cis-Retinal
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The thermally induced sigmatropic hydrogen shift of vinylallene 5 provided a route to highly hindered 11-cis-retinoids.The coupling ot the hetero cuprate 14 with the propargyl benzoate 13b gave the vinylallene 5, which upon heating (69 deg C, 2 h) gave three geometrically isomeric retinoids: 11-sis (8), 11-cis,13-cis (9), and 9-cis,11-cis,13-cis (11).The fourth possible geometric isomer, 9-cis,11-cis (10), was unstable to the conditions of thermolysis and underwent further electrocyclizations to the tricyclic compound 22.The thermal rearramgement of 9,10-allene 5, though highly specific for the formation of 11-cis-retinoids, exhibits no selectivity in the formation of Δ9 and Δ13 double bonds.The highly hindered 11-cis,13-cis- and 9-cis,11-cis,13-cis-retinals, 9b and 11b, exhibit extraordinary electronic absorption spectra in that they exhibit their main maxima (302 nm) actually to the blue of the corresponding alcohols.The retinals 9b and 11b were thermally unstable and underwent clean isomerization to 13-cis-retinal and 9-cis,13-cis-retinal, respectively.
- Knudsen, Christopher G.,Chandraratna, Roshantha A. S.,Walkeapaeae, Leslie P.,Chauhan, Yeshpal S.,Carey, Stephen C.,et al.
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p. 1626 - 1631
(2007/10/02)
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- PHOTOISOMERIZATION OF THE C18 KETONE IN THE VITAMIN A SERIES. SOLVENT EFFECT ON PHOTOISOMERIZATION OF COMPOUNDS RELATED TO RETINAL
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The directions of photoisomerization of polyenals and polyenones are believed to be controlled by the relative ordering of n,?* and ?,?* states.
- Ramamurthy, V.,Denny, M.,Liu, R. S. H.
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p. 2463 - 2466
(2007/10/02)
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- Transient Phenomena in the Pulse Radiolysis of Retinyl Polyenes. 1. Radical Anions
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The spectra and kinetics of formation and decay of radical anions of a number of retinyl polyenes have been studied in methanol and 2-propanol at room temperature, using pulse radiolysis and kinetic spectrophotometry.The bimolecular rate constants for the attachment of solvated electrons, e-MeOH, to the retinyl polyenes are in the diffusion-controlled limit (8.6 x 109-1.6 x 1010 M-1 s-1).The radical anions of retinol and retinol acetate have their spectral maxima at 370-390 nm, and undergo decay very slowly with second-order kinetics.On the other hand, the radical anions of retinal, retinal n-butylamine Schiff base, and retinoic acid/ester have spectral maxima at 430-510 nm, and decay by first-order kinetics in methanol with rate constants in the range 1 x 104-1 x 106 s-1.The decay rates of radical anions of retinal and retinoic acid/ester become considerably longer on going from methanol to less acidic alcohol, 2-propanol, suggesting that protonation by solvent is the major mode of their decay in protic media.In the case of retinal Schiff base, an additional slow process with bimolecular rate constant 9.0 x 107 M-1 s-1 im methanol is observed for the formation of radical anion and is ascribed to the electron-transfer reaction from the methanol radical, .CH2OH.
- Raghavan, N.V.,Das, P.K.,Bobrowski, K.
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p. 4569 - 4573
(2007/10/02)
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